The present invention relates to method and apparatus for applying a predetermined pattern of add-on material to a base web, preferably in the form of stripes, and more particularly, to a method and apparatus for producing cigarettes papers having banded regions of additional material.
Techniques have been developed for printing or coating paper webs with patterns of additional material. These prior techniques have included printing with gravure presses, blade coating, roller coating, silkscreening and stenciling.
U.S. Pat. No. 4,968,534 to Bogardy describes a stenciling apparatus wherein a continuous stencil comes into intimate contact with a paper web during application of an ink or the like. The apparatus includes an arrangement which draws air through the stencil prior to the application of the ink. The mechanical arrangement is such that to change the pattern, the stencil must be changed. Additionally, such apparatus are unworkable at the wet-end of paper-making machines.
In the related, commonly assigned U.S. Pat. No. 5,534,114, an embodiment of a moving orifice applicator is disclosed which includes an elongate xe2x80x9ccavity blockxe2x80x9d or chamber and a perforated endless belt whose lower traverse passes along the bottom portion of the chamber. The chamber is positioned obliquely across a web-forming device (such as a Fourdrinier wire). In operation, a slurry of additional material is continuously supplied to the chamber as the endless belt is looped through the bottom portion of the chamber such that plural streams of material are generated from beneath the chamber to impinge the web passing beneath the chamber. As a result, bands of additional material are applied repetitively to the web. The orientation, width, thickness and spacing of the bands are all determinable by the relative speed and orientation of the endless belt to the moving web.
Preferably, the pattern of additional material is applied as uniformly as possible so as to render consistent product across the entire span of the web. Commonly assigned U.S. Pat. No. 5,997,691 discloses a slurry applicator which can be used with Fourdrinier machines having a width of 10 to 20 feet or more.
In the cigarette papermaking art, it is conventional to convey the sheet of paper on a Fourdrinier papermaking machine at speeds of 1200 to 1400 feet/minute. In contrast, in making sheet paper such as wrapping paper, writing paper and the like, the machine is run at speeds of about 2500 feet/minute. Specialty paper is run at slower speeds. Banded paper such as that described in commonly owned U.S. Pat. Nos. 5,417,228; 5,474,095; and 5,534,114 (see also commonly owned European Pat. Publication Nos. 486213 A1, 532193 A1 and 559453 A1), the disclosures of which including characteristics of the banded paper and papermaking techniques are hereby incorporated by reference, has been produced at speeds of 400 to 600 feet/minute. In practice, banded cigarette paper having 5 to 6 mm wide bands of add-on slurry material has been produced on a Fourdrinier machine at speeds of about 500 feet/minute using a moving orifice device wherein the belt has {fraction (3/32)} inch diameter round holes. It has been discovered that when the speed of the paper sheet is increased, the band widths increase due to the high speed and higher stock flow of the material used to create the bands. It has also been discovered that reduction in stock flow for purposes of reducing band width results in lowered add-on weight of the banded regions. In order to increase production output, it would be desirable to provide a moving orifice applicator which achieves a desired band width and add-on weight at high production speeds.
Accordingly, it is an object of the present invention to provide uniformity in the application of a slurry from a moving orifice applicator onto a sheet traveling at high speed.
It is another object of the present invention to apply bands of slurry material to the sheet with band width and add-on weight within predetermined tolerance levels.
These and other objects are achieved with the present invention whose aspects include a method and apparatus for the production of a web having banded regions of add-on material, more particularly a cigarette paper having stripes of additional cellulosic material added thereto. A preferred method includes the steps of establishing a first slurry, and preparing a base web by laying the first slurry into a sheet form while moving the base web sheet along a first path. The method further comprises the steps of preparing a second slurry and repetitively discharging the second slurry so as to establish stripes upon the base web. The last step itself includes the steps of establishing a reservoir of the second slurry across the first path, moving a belt having slotted orifices along an endless path, which path includes an endless path portion along the reservoir where the orifices are communicated with the reservoir, and discharging the second slurry from the reservoir through the orifices onto the laid first slurry.